1. Field of the Invention
This invention relates generally to a technique for attaching a ferrule to a fiber optic cable and, more particularly, to a technique for attaching a ferrule to a fiber optic cable that employs a cold welding operation.
2. Discussion of the Related Art
Certain photonic devices, such as photodetectors, laser diodes and optical modulators, are sometimes mounted within a housing or device module as part of a device package assembly. A fiber optic cable, including a coaxially formed fiber jacket and optical fiber, is mounted to the module and is aligned with the photonic device. The optical fiber either delivers an optical signal to the photonic device or receives an optical signal generated by the optical device for transmission. The optical fiber can be a single mode fiber, and sometimes a polarization maintaining single mode fiber, requiring high precision optical coupling between the photonic device and the optical fiber, sometimes with submicron accuracy. Sometimes a lens is employed between the photonic device and the optical fiber to provide efficient optical coupling therebetween to reduce optical losses. The fiber optic cable is sometimes attached to a specialized optical adaptor outside the module to be coupled to a suitable optical system.
Because the cable is flexible and has a very small diameter, a ferrule is used to hold the fiber at the desired location to provide proper alignment between the photonic device and an end of the optical fiber. The fiber cable is inserted into the ferrule so that the optical fiber extends out of an end of the ferrule. The ferrule is then positioned within an orifice in the module and mounted thereto so that an end of the fiber is positioned proximate to and aligned with the photonic device. When the fiber is in the desired location, the ferrule is secured to the module by laser welds or by epoxy. Automated alignment and laser welding systems are known in the art, such as the Newport Corporation laser weld work station (LWWS), that provide the desired alignment accuracy. The fiber optic cable is secured to the ferrule and the ferrule is secured to the module in a manner that provides a hermetic seal so that the photonic device is not contaminated by the environment.
Various techniques are known in the art for securing the fiber optic cable to the ferrule. One conventional technique is to glue the fiber optic cable to the ferrule with an epoxy that contains an organic resin. The epoxy is cured at a temperature of approximately 150-165xc2x0 C. to provide the bond. However, the heat of the curing process acts to deteriorate the fiber jacket around the optical fiber which reduces fiber protection. Additionally, the curing process causes the organic resin to generate out-gassing into the ferrule which decreases it hermetic integrity.
To overcome the drawbacks of the epoxy process, it is known to employ a soldering technique to secure the fiber optic cable to the ferrule, where the ferrule is soldered to the optic fiber cable. However, the soldering technique dissipates heat from the soldering point to the fiber jacket that causes the jacket polymer to melt and deform reducing its integrity. Further, both the epoxy technique and the soldering technique are labor intensive, increasing the manufacturing costs.
In accordance with the teaching of the present invention, a cold welding technique is employed for securing a fiber optic cable to a ferrule. The fiber optic cable is inserted into a sleeve so that an end of an optical fiber therein is substantially flush with an end of the sleeve. The fiber optic cable and sleeve assembly is then slid into a sleeve bore through one end of the ferrule so that the fiber is aligned with a narrow fiber bore in the ferrule. The fiber cable is then pushed through the sleeve so that the fiber extends through the fiber bore and out of an opposite end of the ferrule. The sleeve is then retracted from the ferrule while maintaining the relative positions of the ferrule and the fiber optic cable. The sleeve, ferrule and fiber cable assembly is then mounted in a fixture that is immersed in a cold plating bath. The cold plating process is performed so that a layer of a suitable plating material is deposited over the end of the ferrule through which the fiber extends so that the fiber optic cable is held within the ferrule, and the ferrule is hermetically sealed. The sleeve is then slid back into the ferrule, and is optically soldered to the fiber jacket of the cable to hold it in the desired location. dr
FIGS. 1-6 show an assembly process for securing a fiber optic cable to a ferrule employing a cold plating technique, according to an embodiment of the present invention;
FIG. 7 is a plan diagram showing the assembled optical cable and ferrule immersed within a cold plating bath;
FIG. 8 is an exploded perspective view of a fixture employed in the cold plating technique of the invention;
FIG. 9 is a reverse exploded perspective view of the fixture shown in FIG. 8;
FIGS. 10-14 show various views of some of the components of the fixture shown in FIGS. 8 and 9;
FIG. 15 is a perspective view of the assembled fixture; and
FIG. 16 is a cross-sectional view of the assembled fixture of the invention, and including a fiber optic cable and ferrule assembly.